1. Field of the Invention
The present invention relates to a nonradiative dielectric waveguide resonator, a nonradiative dielectric waveguide filter, a duplexer and a transceiver incorporating the same, used in a motor-vehicle-mounted radar in the millimeter wave band and the microwave band, wireless LAN, or the like.
2. Description of the Related Art
A description will be given of a conventional nonradiative dielectric waveguide filter referring to FIG. 23. FIG. 23 is a perspective view of a conventional nonradiative dielectric waveguide filter, in which the upper conductor plate is omitted for convenience sake.
The filter 110a is composed of parallel upper and lower conductor plates 111 made of aluminum, etc., and a dielectric strip 112 made of polytetrafluoroethylene, etc., which is disposed between the upper and lower conductor plates 111. The dielectric strip 112 is composed of resonator parts 115 and input-output connection unit parts 116, which are arranged apart from each other. The resonator parts 115 of the dielectric strip 112 and the upper and lower conductor plates 111 form a nonradiative dielectric waveguide resonator, whereas the input-output connection unit parts 116 of the dielectric strip 112 and the upper and lower conductor plates 111 form input-output connection units.
In the nonradiative dielectric waveguide, the distance between the upper and lower conductor plates 111 is set to no more than a half wavelength of the frequency used. This permits a position in which the dielectric strip 112 is present to be a signal-transmitting region and permits a position in which the dielectric strip 112 is not present to be a cut-off region. Thus, signals transmitting through the input-output connection unit couple to the nonradiative dielectric waveguide resonator through the distance between the input-output connection unit parts 116 and the resonator parts 115 of the dielectric strip 112 so as to resonate with a resonance frequency determined, for example, by the length of the signal-transmitting direction of the dielectric strip 112. After coupling to the input-output connection unit, signals are output, in which the nonradiative dielectric waveguide filter 110a acts as a band pass filter.
Additionally, a description of another conventional embodiment will be provided referring to a perspective view of FIG. 24. The same reference numerals are given to the same parts as those in the first conventional embodiment, and only a brief explanation is given.
As shown in FIG. 24, the nonradiative dielectric waveguide filter 110b employed in a second conventional embodiment is also composed of the upper and lower conductor plates 111 and the dielectric strip 112 disposed between the upper and lower conductor plates 111. In this embodiment, the resonator parts 115 and the input-output connection unit parts 116 of the dielectric strip 112 are connected by a dielectric strip having a narrower width. When the width is significantly narrowed as shown in FIG. 24, the part is allowed to be a cut-off region. Thus, the nonradiative dielectric waveguide filter 110b shown in FIG. 24 also acts as a band pass filter, as in the case of the first conventional embodiment.
Primarily, in a nonradiative dielectric waveguide filter, the length of the signal-transmitting direction of a resonator part of a dielectric strip determines a resonance frequency, the distance between resonator parts determines a coefficient of coupling, and the distance between an input-output connection unit part and the resonator part determines an external Q.
In the first conventional embodiment, however, the resonator part and the input-output connection unit part of the dielectric strip are arranged apart from each other. As a result, fine adjustment between their arranged positions is necessary to obtain required characteristics. Furthermore, even after the formation of the nonradiative dielectric waveguide filter, for example, shocks from the outside cause changes in their arranged positions so that filter characteristics are also changed.
Meanwhile, in the second conventional embodiment, since the resonator part and the input-output connection unit part of the dielectric strip are connected, their arranged positions are not likely to change. However, it is difficult to manufacture such an approximately 1-2 mm wide dielectric strip so as to make it compliant with required filter characteristics.